A wireless communication system includes base stations providing a wireless access in a cell of a predefined range. The base station may be denoted by a different name depending on a standard of a system. Since each base station provides a wireless access to a terminal positioned inside a cell, when the terminal moves from a cell of one base station to a cell of another base station, a handover may be performed in order to provide continuity of a service. Though the wireless communication system may provide service continuity via the handover, the following problem may occur depending on a point at which a serving base station changes by the handover.
Recently, as a call service using packet communication, Voice over Internet Protocol (VoIP) is in the limelight. Generally, Session Initiation Protocol (SIP) is used as a call control protocol of the VoIP. Since a base station does not get involved signaling related to the SIP, it does not know a VoIP call setup procedure is in process before a VoIP bearer is set. Therefore, while the VoIP call setup procedure is triggered from a terminal or a network and is in progress, when a condition for performing a handover is met, the base station proceeds with a handover procedure.
As described above, even when the VoIP call setup procedure is in process, a handover procedure may be performed. In this embodiment, the base station receives a message for the VoIP bearer setup while the handover procedure is in progress. However, since the handover procedure is in progress already, the base station cannot process the VoIP bearer setup. That is, the VoIP bearer setup fails. Accordingly, the terminal accesses a target base station, and then should perform the VoIP bearer setup procedure again. That is, a delay in the VoIP bearer setup may occur due to the handover procedure.